This invention relates to target wheels for speed sensors used to determine the rotational speed of a bearing, axle, or the like, and, in particular, to a target wheel with improved retention capabilities.
The rotational speed of a bearing or axle is important in many applications. For example, anti-lock brake systems (ABS) rely on sensors which monitor the rotational rate of the bearing (and hence of the vehicle wheel) in controlling ABS. The sensing system typically includes a target wheel which rotates with the rotating portion of the bearing and a sensor. Prior art target wheels are shown, for example, in U.S. Pat. Nos. 5,085,519 and 5,816,711, which are incorporated herein by reference. When applied to the bearing inner race, the target wheel is press fit onto the bearing inner race with a press fit of approximately 0.02 mm to approximately 0.15 mm. Until recently, these target wheels have been solid steel or powdered metal designs where the fit of the target wheel is constant across its width. More recently, stamped target wheels are being considered for applications internal to the bearing.
Stamped target wheels generally have a C-shape, as seen in FIG. 1. Such target wheels include a base 1 which is bent, as at 3. Encoding means, in the form of a plurality of spaced apart ribs or teeth 5, extend from the bend 3. With this design, the fit is not constant across the width of the target wheel. There is generally a single annular or circumferential line of contact between the target wheel and the bearing inner race 7 under the bend 3. The fit of the stamped target wheel T on the bearing inner race decreases along the length of the base 1 of the target wheel T. Due to the fit of the target wheel T on the bearing inner race 7, under a dynamic load condition, the target wheel T can walk across the cone or inner race 7. This results in (1) a change in the gap between the sensor and the target wheel; and (2) a possible loss of the sensor signal. Both of these results are undesirable.